Fluid flow control valves are used in applications where the valve internals are subjected to corrosive acidic or caustic liquids, or where the purity of the liquids which flow through the valve must be maintained. An example of such application is the semi-conductor manufacturing industry where process chemicals distributed through a control valve must maintain a high degree of chemical purity to avoid contamination that may occur on the microscopic level. Such valves are either constructed of relatively inert materials, e.g., fluoropolymers or other polymeric materials, or the valve surfaces which come into contact with the flowing liquids, or which potentially can come into contact with the liquids, are coated with such inert materials.
Fluid flow control valves known in the art are commonly biased into the closed position by a spring force and are opened by means of a solenoid actuator, or actuator means operated by pneumatic or hydraulic pressure and the like. Valve closure springs typically used in such valves are made from a metallic material and configured to afford a resilient action. Such fluid control valves also include at least one diaphragm disposed within the valve chamber of the valve. The diaphragm is placed into contact with the liquid and serves to prevent the escape of the fluid from the valve chamber into the valve operating mechanism and into the environment. A valve stem is disposed axially within the chamber and the diaphragm is attached to an end of the valve stem, thereby forming a valve poppet assembly. The diaphragm includes a peripheral edge portion that is engaged against an adjacent wall portion of the valve body at each opposite end of the valve body.
The valve closure springs are typically placed adjacent a surface of the valve diaphragm that is not exposed to the process fluid distributed through the valve. The transfer of the process fluid through the valve is controlled by the actuation of the valve stem within the chamber against a valve seat. The movement of the valve stem is accommodated in part by the controlled deformation of the diaphragm. Control valves constructed in this manner are prone to failure due to both the possibility of eventual diaphragm rupture and to the large number of leak paths inherent in such construction. A valve constructed in this manner has two leak paths or potential passages through which fluid within the valve chamber can escape into the valve operating mechanism or the environment. One leak path is formed at the attachment point between the diaphragm and the end of the valve stem, and the other leak path is formed between the peripheral edge of each diaphragm and the valve body walls.
Diaphragm rupture or leakage though any one of the leak paths is not desirable because the process chemical directed through the valve chamber may be allowed to escape into the valve body where the corrosive or caustic chemical can come into contact with the valve spring, and thereby provide a source of ionic contamination to the process chemical to pass on to other downstream chemical processing units. Alternatively, diaphragm rupture or leakage may result in the escape of the process chemical from the valve chamber, through the valve body and onto the ground or into the atmosphere, where the particular process chemical may cause a hazard to the environment or a health danger to nearby operators.
The potential for diaphragm rupture or leakage limits the extent to which such valves can be used in high process pressure or high process temperature applications. The diaphragm used in such valves is designed to both permit a desired degree of elastic deformation to permit valve stem actuation and provide a barrier to prevent unwanted process fluid migration from the valve chamber into an actuating chamber of the valve. Although ultimate barrier performance of the diaphragm can be achieved by maximizing its thickness, a maximum diaphragm thickness is governed by the competing need to provide a diaphragm that is capable of elastically deforming a desired amount to ensure valve stem actuation. It is this need to keep the diaphragm deformable that also limits the temperature and pressure at which the valve can safely operate, it being understood that the maximum operating pressures and temperatures for the valve are related.
The construction of a fluid flow control valve having a poppet assembly constructed using such valve stem and diaphragm members impacts the size of the valve itself, as the stroke length of the valve stem is closely related to the diameter of the diaphragm. Generally speaking, the longer the desired valve stem stroke length, the larger the diameter of the diaphragm to enable such stroke length. Additionally, the size of a particular valve that is adapted to operate to a certain maximum pressure and temperature will depend, inter alia, on the size of the diaphragm that is needed to provide adequate deformation and barrier performance characteristics. Generally speaking, the more highly rated the valve, i.e., the higher the flow, the larger the valve itself due in part to the need to provide a diaphragm suitably sized to withstand such flow conditions.
In the handling of fluids where the space occupied by the fluid handling apparatus or valve apparatus in a fluid handling system is at a premium, it is desired that such valve apparatus be compact or small in size. In the handling of liquids where the chemical purity must be maintained, to ensure the desired degree of quality for the product manufactured using such process liquids, and the escape of process liquids into the environment is undesired, it is desired that the valve apparatus be made in a manner that both: (1) eliminates the possibility that contaminants may be introduced into the process caused by contact of the process liquid with elements of the valve during distribution therethrough; and (2) minimizes the possibility of process liquid escaping from the valve chamber into other portions of the valve or into the environment.
It is desirable that the valve apparatus be constructed having a compact size that is smaller than conventional diaphragm or poppet-type valves designed to operate at the same flow conditions. It is desirable that the valve apparatus be made from material having a high degree of chemical resistance and thermal resistance to resist degradation through contact with corrosive, or caustic chemicals and the like. It is desirable that the valve apparatus be constructed in a manner that results in the inherent reduction of leak paths, thereby minimizing the potential for chemical leakage into the environment. It is desirable that the valve apparatus be capable of operating at high temperatures and under high pressures without danger of valve failure or chemical leakage. It is also desirable that the valve apparatus be constructed using conventional manufacturing principles from available materials to reduce the cost of manufacturing such valve.